Although not limited thereto, this process has particular value for working the longitudinal grooves used as capillaries in the casings of heat pipes. The term heat pipe refers to a well-known class of heat transfer devices that comprise a closed casing, a liquid transport means and a vaporizable liquid. The heat pipe operates by having a heat input region wherein the vaporizable liquid boils and changes to the vapor state and a heat rejection region where the vapor is condensed to a liquid. The liquid is returned to the heat input region by the liquid transport means which may comprise a grooved longitudinal or annular capillary wall, a screen mesh artery or a combination of both of those devices.
The present invention provides a process that can be used in the manufacture of a heat pipe having an improved longitudinal grooved capillary wall wherein the grooves have an opening that is smaller than the width of the groove and the lands between the grooves have mushroom-shaped cross-sections. This structure provides a heat pipe that will hold liquid in all of its longitudinal grooves, both top and bottom. This heat pipe will have good "tilt" capability due to the capillary action in the grooves which have a narrow opening. Grooves of this configuration will also insure that the heat pipe will have good flow and filling characteristics due to the venting and capillary action of the narrow opening of the grooves. If the grooves are not completely full, the vaporizable liquid in the narrow-opening grooves will tend to flow up the side walls by film action, and feed into the opening of the grooves.
In the condensing region of the heat pipe, the narrow groove openings act as wicks, attracting and sucking the condensing vapor into the grooves. The lands between the grooves of a heat pipe made according to this invention also contribute to an increased thermal efficiency as the mushroom shape of the lands results in a greater surface area being exposed to the vaporizable liquid, especially in the areas where nucleate boiling and/or film vaporization normally take place.